Various scientific and scholarly articles are cited throughout the specification. These articles are incorporated by reference herein to describe the state of the art to which this invention pertains.
The reversible phosphorylation of proteins and lipids is critical to the control of signal transduction in mammalian cells and is regulated by kinases and phosphatases (Hunter 1995). The product of the tumor suppressor gene PTEN/MMAC (hereafter termed PTEN) was identified as a dual specificity phosphatase and has been shown to dephosphorylate inositol phospholipids in vivo (Li et al Science 1997, Steck et al 1997, Li et al Cancer Res 1997, Myers et al, 1997, Myers et al 1998, Maehama et al, 1998, Stambolic et al 1998, Wu et al 1998). The PTEN gene, which is located on the short arm of chromosome 10 (10q23), is mutated in 40-50% of high grade gliomas as well as many other tumor types, including those of the prostate, endometrium, breast, and lung (Li et al, Science 1997, Steck et al 1997, Maier et al 1998). In addition, PTEN is mutated in several rare autosomal dominant cancer predisposition syndromes, including Cowden disease, Lhermitte-Duclos disease and Bannayan-Zonana syndrome (Liaw et al 1997, Myers et al AJHG 1997, Maehama et al TCB 1999, Cantley and Neel 1999). Furthermore, the phenotype of PTEN-knockout mice revealed a requirement for this phosphatase in normal development and confirmed its role as a tumor suppressor (Podsypanina et al PNAS 1999, Suzuki et al Curr Biol 1998, Di Christofano et al Nat Gen 1998).
PTEN is a 55 kDa protein comprising an N-terminal catalytic domain, identified as a segment with homology to the cytoskeletal protein tensin and containing the sequence HC(X)5R, which is the signature motif of members of the protein tyrosine phosphatase family, and a C-terminal C2 domain with lipid-binding and membrane-targeting functions (Lee et al Cell 1999). The sequence at the extreme C-terminus of PTEN is similar to sequences known to have binding affinity for PDZ domain-containing proteins. PTEN is a dual specificity phosphatase that displays a pronounced preference for acidic substrates (Myers et al PNAS 1997). Importantly, PTEN possesses lipid phosphatase activity, preferentially dephosphorylating phosphoinositides at the D3 position of the inositol ring. It is one of two enzymes known to dephosphorylate the D3 position in inositol phospholipids.
Since solid tumor progression is dependent on the induction of angiogenic signals and augmented angiogenesis contributes to the high mortality associated with many cancers, there is a need to elucidate the cellular components that participate in these processes. The urgency of such investigations is underscored by the fatal nature of highly malignant brain tumors and the fact that the degree of tumor invasiveness is directly correlated with enhanced angiogenesis. Furthermore, elucidation of cellular components that contribute to the angiogenic switch facilitates the identification of therapeutic agents and delivery methods useful for the treatment of such malignant diseases.
PTEN phosphatase activity has also been implicated in many cellular biochemical reactions. It is an object of the invention to also provide methods for the identification of agents which impact PTEN modulation of immunoreceptors, AKT, PI3 kinase and p53 signaling. Methods of use of agents so identified are also within the scope of the invention.